The particular application of the preferred embodiment of the present invention is in the application of electric motors to power steering systems for motor vehicles. Most power steering systems are hydraulic and as such require large amounts of power from the engine. Electric power steering systems use a reversible electric motor as the prime mover and as such the horsepower drain from the engine is reduced.
It is a particular advantage of this invention to provide a control system for reversing the rotation of the electric motor. In addition it is an another advantage of the control system to provide failure detection modes which are communicable to the vehicle operator notifying him to take any necessary service steps.
These and other advantages are found in a control system for reversing the rotation of a field wound motor having a field winding and an armature winding, each electrically connected at one end to a source of electric power. A control means generates control signals to select the rotation of the motor and to energize the armature winding. An armature power driver circuit is electrically connected to the armature winding and responds to one of the control signals to energize the armature winding to control the flow and amount of current through the armature winding. A field winding power driver is electrically connected in a bridge circuit with the field winding across the center of the bridge. The field winding power driver is responsive to another of the control signals to select the rotation of the motor by controlling the direction and amount of the flow of current through the motor field winding.
The several control signals applied to the control system are compared with the results of the system and if there is not concurrence, a failure signal is generated. The utilization of the failure signal is under the control of the overall electric power steering system control.
These and other advantages will become apparent from the following detailed description taken in conjunction with the drawings.